Gemc

Gemc lets you prepare CD image files (such as BIN, CDI, NRG, CCD, or similar) so that they'll compress far better in programs such as WinRAR.

HERE`S HOW TO USE IT:
Run the CD image file (i.e. filename.bin) through GEMC to create an ECM file (i.e. filename.bin.ecm).

Compress the ECM file (i.e. filename.bin.ecm) using your favorite compression program (i.e. 7Z,RAR,ZIP..).

Back up, transmit via Internet, or whatever you normally do with CD images!
When you want to burn the CD again, extract the original CD image from the ECM file.

space saved depends on the number of sectors with unnecessary EDC/ECC data in them, which will depend on the specific type of CD